1. Field of the Invention
The present invention generally relates to apparatus for measuring or compensating for time delays or phase differences and, more particularly, relates to apparatus for measuring, or compensating for, time delays or phase differences between two electrical signals where one electrical signal can either lead or lag the other electrical signal.
2. Description of the Prior Art
There are numerous signal processing applications which require estimation of the difference in phase or difference in time of occurrence (both collectively referred to hereinafter as phase difference) between two time-varying signals, such as between a reference signal and another version of the reference signal which has undergone a phase shift due to a transmission or processing medium. Often such phase shift will take the form of a time delay, and arrangements are known for measuring or compensating for this condition. However, many applications must accommodate the condition where the desired signal may either lead or lag the reference signal. If compensation is required, it is desirable that it be performed adaptively.
To facilitate an understanding of the application of the invention and the shortcomings of the prior art, several examples will be considered.